An AC-type surface discharge plasma display panel has become dominance in plasma display panels (hereinafter simply referred to as a panel). A panel contains a front plate and a rear plate oppositely disposed with each other and a plurality of discharge cells therebetween. On the front plate, a plurality of display electrode pairs, each made of a scan electrode and a sustain electrode, are formed on a front glass substrate in parallel with each other. A dielectric layer and a protective layer are formed to cover these display electrode pairs. On the rear plate, a plurality of data electrodes are disposed in a parallel arrangement, and over which, a dielectric layer is formed to cover the data electrodes. On the dielectric layer, barrier ribs are formed in parallel with the data electrodes. A phosphor layer is formed on the dielectric layer and on the side surfaces of the barrier ribs. The front plate and the back plate are sealed with each other so that the display electrode pairs are orthogonal to the data electrodes in a discharge space between the two plates. The discharge space is filled with discharge gas, for example, a gas containing 5% xenon in a ratio of partial pressure. The discharge cells are formed at which the display electrode pairs face data electrodes. In the panel structured above, a gas discharge occurs in each discharge cell and generates ultraviolet light, which excites phosphors for red (R), green (G) and blue (B) to generate visible light of respective colors.
In the typical panel operation, one-field is divided into a plurality of sub-fields, which is known as a sub-field method. According to the sub-field method, gradation display on the panel is attained by combination of the sub-fields to be lit.
Each sub-field has an initializing period, an address period and a sustain period. In the initializing period, an initializing discharge occurs in the discharge cells. The initializing discharge generates wall charge on each electrode as a preparation for an address operation in the address period that follows the initializing period; at the same time, the initializing discharge generates a priming particle (as an initiating agent, i.e., an excitation particle). In the address period, an address discharge selectively occurs in a cell to be ON to form the wall charge (hereinafter, the operation may be referred to as an address operation) by applying address pulses. In the sustain period, sustain pulses are alternately applied between the scan electrodes and the sustain electrodes of the display electrode pairs. The applied pulses generates a sustain discharge in the cells in which the wall charges have been formed in the previous address discharge and excites the phosphor layer of the cells. Through the process above, image is shown on the panel.
In the sub-field methods, a suggestion on improvement has been made. According to the disclosure, after generating an initializing discharge by applying a gradually varying waveform voltage, another initializing discharge is selectively generated in the discharge cell where an address discharge occurred in the address period. The driving method can suppress light-emitting with no contribution to gradation display and therefore improves contrast ratio.
According to the method above, an initializing operation in which the initializing discharge occurs in all the discharge cells (hereinafter, all-cell initializing operation) is carried out in the initializing period of one sub-field in a plurality of sub-fields. In the rest of the sub-fields, the initializing discharge is selectively generated only in a cell where a sustain discharge occurred in the previous sustain period (hereinafter, selective-cell initializing operation). Driving a panel with the method above can suppress unwanted light-emitting with no contribution to gradation display. That is, the area being responsible for black color (hereinafter, black luminance) has substantially no light-emission except for a weak emission caused by the all-cell initializing operation, so that contrast ratio in image greatly improves (see patent reference 1, for example).
Besides, patent reference 1 describes an efficient use of sustain pulses having a width narrower than that of other sustain pulses, known as a narrow-width erase discharge. Applying the narrow-width sustain pulses at the end of the sustain period reduces difference in voltage between the display electrode pairs that is caused by wall charges. Maintaining stability of the narrow-width erase discharge ensures reliable address operations in the address period of the successive sub-field, allowing a plasma display device to have high contrast ratio.
As a recent trend of panels that become larger in size and higher in resolution, manufacturers are seeking for further excellent image display. Providing a panel with higher emission luminance allows the panel to have excellent image quality. To obtain higher luminance, increasing the ratio of xenon partial pressure is known as an effective way. Increase in the partial pressure ratio of xenon, however, also increases voltage required for address operations, which has often led unstable address operations. Besides, characteristics of a panel vary according to cumulative time of current-carrying panel (hereinafter, cumulative current-carrying time). Increase in cumulative current-carrying time also increases address pulse voltage for generating a stable address discharge. That is, for stable address operations, address pulse voltage has to be set higher for longer cumulative current-carrying time of a panel.    patent reference 1: Japanese Unexamined Patent Application Publication No. 2000-242224